Endoscopes have been used for many years in the medical field to look within a selected region of a patient's body, e.g., the colon or the upper gastrointestinal region. The endoscope is typically inserted through an orifice or a surgical incision into a body channel or cavity. Endoscopes are commonly used to perform surgical, therapeutic, diagnostic, or other medical procedures under direct visualization. Conventional endoscopes generally contain several endoscope components, such as fiber optic light guides, a fiber optic image guide, and a working channel. The endoscope can also be equipped with one or more instrument channels for surgical implements. These components are positioned within the lumen of an endoscope sheathing tube. Endoscopes may be rigid or flexible. Flexible endoscopes incorporate an elongated flexible shaft and may include an articulating distal tip to facilitate navigation through the internal curvature of a body cavity or channel. Examples of conventional endoscope designs are described in U.S. Pat. Nos. 4,706,656; 4,911,148; and 5,704,899.
In order to facilitate endoscopic procedures, patients often receive sedation. In recent years, fast acting sedation drugs, such as intravenous propofol, have been used in conjunction with endoscopic procedures. The use of sedation has required increased reliance on the use of monitoring devices to detect early signs of patient distress, such as heart rate, transcutaneous PCO2, EKG and EEG for monitoring heart and brain functions, respectively, during surgery. The risk for patient respiratory distress, such as shock, is increased by any procedure that requires the use of a strong sedative, for example, in upper GI endoscopic procedures, such as endoscope retrograde cholangiopancreatography (“ERCP”), especially in frail patients.
While the conventional monitoring techniques work well for their intended use, they are not well suited for monitoring respiratory distress during various endoscopic procedures. One means of monitoring the respiratory status of a patient undergoing an endoscopic procedure is by measuring and charting the concentration of CO2 in the patient's expired air, during the end-tidal phase (ETCO2) of the respiratory cycle, in a procedure known as capnography. The capnographic unit is typically attached to a mask fitted over the patient's airway. However, a more sensitive means for measuring expired CO2 is needed to provide early detection of patient respiratory distress during endoscopy.